Quick read paging3 source code by AI tool

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Google NotebookLM is the sharp AI spear, Android Paging3 lib is the tough shield.
Let break this shield using the spear to learn.

Context

Paging3 is a complicate Android lib with a bunch of classes to do the paging stuff, although it hard to understand and use, but we use it for now and need to known the details. The article here introduce a way to read and understand the lib source code quickly by leveraging the AI tool of Google NotebookLM.

The initial purpose it to understand how the prepend loading is triggered, is it able to manually triggered with flexibility, while dive deep into it, it really deep to follow, lots of classes and concepts is defined to achieve the purpose. NotebookLM come rescue me from the headache.

By pasting all the source code to it as context, it knowns relationship between classes, it explains concept well. It even draw the nice diagrams with little modified input. And the most detailed and accurate is the explanation of the functions.

Preparation

  1. Download all the paging3 source code using https://downgit.github.io/#/home
  2. Use copy-files-to-clipboard-for-llm plugin to merge all the files and copy to clipboard
  3. Paste the source code to NotebookLM as the reference source
  4. Chat with NotebookLM for your need

Chat to learn

Here I will list some core questions to figure out the prepend triggering flow and related concepts defined by the lib.








Summerize diagram

Q8-1 draw a sequence diagram to present the the flow of prepend loading
Q8-2 add LazyPageingItems in the sequence diagra


sequenceDiagram

participant UI

participant LazyPagingItems

participant PagingDataPresenter

participant HintReceiver

participant PageFetcher

participant PageFetcherSnapshot

participant PageFetcherSnapshotState

participant PagingSource

UI->>LazyPagingItems: Access item (get)

activate UI

activate LazyPagingItems

LazyPagingItems->>PagingDataPresenter: Get item at index (get)

activate PagingDataPresenter

PagingDataPresenter->>PagingDataPresenter: Get item from page store

PagingDataPresenter->>HintReceiver: Access Hint (ViewportHint)

deactivate UI

activate HintReceiver

HintReceiver->>PageFetcher: Access Hint (ViewportHint)

deactivate HintReceiver

activate PageFetcher

PageFetcher->>PageFetcherSnapshot: Access Hint (ViewportHint)

activate PageFetcherSnapshot

PageFetcherSnapshot->>PageFetcherSnapshot: Wrap hint with generationId (GenerationalViewportHint)

PageFetcherSnapshot->>PageFetcherSnapshotState: Get next load key (nextLoadKeyOrNull)

activate PageFetcherSnapshotState

PageFetcherSnapshotState-->>PageFetcherSnapshot: Return load key

deactivate PageFetcherSnapshotState

alt Valid load key and prefetch distance not fulfilled

PageFetcherSnapshot->>PagingSource: Load data (load, LoadParams{loadType=PREPEND, key, loadSize})

activate PagingSource

PagingSource->>PagingSource: Fetch data

PagingSource-->>PageFetcherSnapshot: Load result (LoadResult{Page/Error})

deactivate PagingSource

PageFetcherSnapshot->>PageFetcherSnapshotState: Insert page, update load state, check for drop (insert)

activate PageFetcherSnapshotState

PageFetcherSnapshotState-->>PageFetcherSnapshot: Confirmation

deactivate PageFetcherSnapshotState

else Load key invalid or prefetch distance fulfilled

PageFetcherSnapshot->>PageFetcherSnapshot: Skip load

end
deactivate PageFetcherSnapshot
deactivate PageFetcher
deactivate PagingDataPresenter
LazyPagingItems-->>UI: Return item
deactivate LazyPagingItems

Q9 draw a class diagram using components in the above sequence diagram


classDiagram

class UI

class LazyPagingItems {
-flow: Flow<PagingData<T>>
-pagingDataPresenter: PagingDataPresenter<T>
+refresh()
+loadState: CombinedLoadStates
+get(index: Int): T?
}


class PagingDataPresenter {
-hintReceiver: HintReceiver
-uiReceiver: UiReceiver
-pageStore: PageStore
+refresh()
+get(index: Int) : T?
+addLoadStateListener(listener)
+removeLoadStateListener(listener)
+presentPagingDataEvent(event: PagingDataEvent)
}


class HintReceiver {
+accessHint(hint: ViewportHint)
}


class PageFetcher {
-snapshot: PageFetcherSnapshot
+refresh()
}


class PageFetcherSnapshot {
-pagingSource: PagingSource
-stateHolder: PageFetcherSnapshotState.Holder
+doLoad(loadType: LoadType, hint: GenerationalViewportHint)
+doInitialLoad()
}


class PageFetcherSnapshotState {
-pages: List<TransformablePage<Key, Value>>
-placeholdersBefore: Int
-placeholdersAfter: Int
+insert(generationId: Int, loadType: LoadType, page: Page) : Boolean
+nextLoadKeyOrNull(loadType: LoadType, generationId: Int, presentedItemsBeyondAnchor: Int) : Key?
}


class PagingSource {
+load(params: LoadParams) : LoadResult
}

UI ..> LazyPagingItems
LazyPagingItems *-- PagingDataPresenter
PagingDataPresenter ..> HintReceiver
HintReceiver ..> PageFetcher
PageFetcher *-- PageFetcherSnapshot
PageFetcherSnapshot *-- PageFetcherSnapshotState
PageFetcherSnapshot ..> PagingSource